Compositions and methods for treating metal surfaces

ABSTRACT

Acidic solutions having as an acidic component phosphoric acid and sulfuric acid, as a surfactant component a mixture of primary ethoxylated alcohol and modified polyethoxylated straight chain alcohol, and as a sequestrant component a mixture of oxalic acid and citric acid, are useful in cleaning aluminum, especially drawn and ironed aluminum cans coated with drawing oil, in cleaning, deoxidizing and brightening stainless steel, and in forming corrosion resistant and paint adherent iron phosphate coatings on ferriferous surfaces when applied thereto by the reverse roll coat method.

United States Patent Hamilton 51 Jan. 18, 1972 [72] Inventor: Andrew J.Hamilton, Philadelphia, Pa.

[54] COMPOSITIONS AND METHODS FOR TREATING METAL SURFACES [73] Assignee:Amchem Products, Inc., Ambler, Pa.

[22] Filed: Nov. 3, 1969 [21] Appl. No.: 873,626

[52] U.S. Cl. ..252/79.4,' 156/3, 156/20, 156/22, 252/791, 148/615,148/6.l7

[51] Int. Cl. ..C23g 1/08, C23g 1/12, C23f 3/00 [58] Field ofSearch..l56/21,22, 20, 3,18; 148/617, 6.15, 6.24; 252/791, 79.2, 79.4; 134/3,

[56] Relerences Cited UNITED STATES PATENTS 2,662,814 12/1953 Swihart..156/20 2,813,816 11/1957 Otto. ..l48/6.17 3,523,835 8/1970 Turneretal...148/6.24

Primary Examiner-Jacob l-l. Steinberg Attorney-Synnestvedt and Lechner[57] ABSTRACT Acidic solutions having as an acidic component phosphoricacid and sulfuric acid, as a surfactant component a mixture of 20Claims, No Drawings cordance with COMPOSITIONS AND METHODS FOR TREATINGMETAL SURFACES This invention relates to novel compositions and methodsfor using them for the treatment of metal surfaces for a variety ofpurposes. The compositions of the present invention have multipleutilities, since they have been found to functionally interact withdifferent types of metal surfaces in different ways to produce differentuseful results. In particular the compositions of the invention areuseful in the acid cleaning of aluminum surfaces, in the deoxidizing andcleaning of stainless steels, and in the production of iron phosphatecoatings on ferriferous surfaces to enhance the corrosion resistance andpaint adhesion properties of such surfaces.

In industry it is necessary to clean aluminum surfaces under a varietyof circumstances, and alkaline and acidiccleaning solutions have longbeen used for such purposes. The severity of the cleaning problem is, ofcourse, greatly influenced by the type of industrial processing that thealuminum has been subjected to prior to cleaning, andthe kind of surfacetreatment, if any, which is to follow the cleaning step.

A particularly severe aluminum cleaning problem is encountered in theproduction of aluminum cans for use as beverage containers, and thecompositions of the present invention are outstandingly effective inthis environment. In acone widely used system for forming aluminum cans,aluminum sheet, with the ordinary accumulations of manufacturing andwarehouse soil on the surface, is subjected to a deep forming operationtermed drawing and ironing. In this operation a water dispersedlubricating oil called a drawing oil" is used to reduce the frictionbetween the tooling and the aluminum being formed into a can. The dirty,oily, can so formed must then be cleaned so that a chemical pretreatmentdesigned to enhance paint bonding and corrosion resistance can beapplied. The chemical pretreatment is then followed by a painting orlacquering operation involving one or more organic siccative finishes.

Some of the factors which make the aluminum can cleaning operation justdescribed a diflicult one to perform successfully can be identified.Cost considerations as a practical matter prohibit the use of anycleaning system in which the cleaning material is used on a once-onlybasis and is immediately flushed to the sewer. Substantially anymaterial which is capable of successfully attacking and removing soilsfrom an aluminum surface will also dissolve some aluminum. Thiscircumstance, coupled with the economic necessity for recycling thecleaner for reuse means that the cleaning bath, as it ages, will containincreasing amounts of dissolved aluminum. At some point, depending uponthe particular chemicals employed in the cleaner and various operatingconditions, insoluble aluminum compounds will tend to drop out of thecleaning solution in the fonn of sludge. Such sludge causes bothcleaning problems and equipment problems. If the sludge redeposits as afilm or smut on the aluminum which has just been cleaned, then theobject of the cleaning operation, to some extent, has been defeated. Theequipment difficulties caused by sludge can include clogging of sprayheads, and the formation of hard scaly deposits on tank heating coilswhich interfere with heat transfer into the bath. Even if such majordifiiculties are avoided, the buildup sludge in the cleaning equipmentdoes require periodic shutdowns for costly sludge removal operations.

Just as most acidic cleaning materials capable of attacking the soils onthe aluminum will also attack the aluminum itself, they will also tosome extent attack the cleaning equipment, that is, the tank, pumps,lines, and spray heads. In most installations, part or all of thisequipment is formed of stainless steel, and it is thus a requirement ofa good aluminum cleaning solution that it have a low rate of attack orcorrosion on stainless steel. The equipment corrosion problem is mostacute at the steam coils or fire tubes in the cleaning tank. The hightemperatures and high local concentrations resulting from localizedboiling or ebullition at the heating element surface are the cause ofthis aggravation of the equipment corrosion problem.

The presence of the above-mentioned drawing oil as a soil on the canswhich are presented to the cleaning solution creates further problems.Such oils are commonly used in the drawing machines as water emulsionswith an oil concentration of about 4 to 14 percent. The emulsion isformed before the oil is delivered to the drawing equipment, and whilethe emulsion remains fairly stable during its residence time in thedrawing equipment, it is not an emulsion with long term stability. Theshort emulsion life of the oil is, in fact, a desired characteristic,since economic considerations sometimes make it attractive to recoverthe oil, after the emulsion has broken, for reuse. Those skilled in theart know that surfactants are often desirable components of a cleaningmaterial, to aid in the wetting of the surface being cleaned, and in theremoval of soils. It is also known that many surfactants contribute tothe establishment of stable emulsions of oil and water. Yet a stableoil-in-water emulsion in the cleaning solution is undesirable. If theoil emulsion is stabilized by the surface-active components of acleaner, the oil concentration will build up as the cleaning solution isrecycled, and the emulsion will eventually tend to break at a relativelyhigh oil concentra tion. Under such circumstances, there is a greatdanger that the breaking of the emulsion will occur when the cleaningsolution is in contact with the aluminum surface. When this occurs, theoil redeposits on the surface, thus partially or wholly defeating theobject of the cleaning. It is thus desired that the cleaning solutionhave a set of surface active properties which meet somewhat incompatibleperformance requirements: the solution should have sufficient activityto lift the emulsified drawing oil (and other soils) from the surface,and at the same time, have a low enough surface activity to enable theunstable drawing oil emulsion to readily break, thus allowing the oil toseparate and float on the surface of the cleaning solution tank, whereit may readily be removed, and thereby prevented from being recycledwith the cleaning solution back to the aluminum surfaces being cleaned.

The type of cleaning equipment which is usually used for cleaningaluminum cans is of the spray type, including a cabinet having spraynozzles in it and a solution tank positioned beneath the cabinet tocatch solution falling from the cans after contacting them. The solutiontank contains the heating element. Solution is pumped from the tankthrough lines to the spray nozzles where it is sprayed against cansbeing conveyed through the cabinet and then falls back into the solutiontank. When a cleaning solution is used in such apparatus it can be seenthat it is subjected to considerable turbulence. For this reason it isdesirable that the solution be of the low-foaming type.

One of the objects of the invention is the provision of compositionscapable of cleaning aluminum, even in the severe cleaning environment ofan aluminum can operation, which compositions overcome all of theproblems outlined above.

The removal of dirt and scale from stainless steel has long beenregarded as a difiicult metal-cleaning problem. In particular, the oxidescales resulting from annealing operations are difficult to removeeffectively and safely. The standard cleaning or pickling solutions ofthe kind that are effective on other kinds of steel, besides being slowacting when applied to stainless steels, also often result in pittingand uneven cleaning, as well as hydrogen embrittlement of the stainlesssteel. The compositions of the present invention are effective to removeoxide from stainless steel surfaces, especially oxide resulting fromannealing, and it has been discovered that they have the added effect ofbrightening the stainless steel following oxide removal. These objectsare accomplished at the same time that the foregoing problems ofselective attack or pitting and hydrogen embrittlement are overcome.

The application of iron phosphate coatings to ferriferous surfaces haslong been practiced for the purpose of imparting corrosion resistanceand good paint-adhesion properties to the ferriferous surface. The arthas developed a variety of formulations of iron phosphate coatingmaterials for use in conventional coating apparatus of the dip or spraytype. A newer method of applying chemically protective coatings tometals has come into wide use recently. This method is known as reverseroll coating. In this connection see US. Pat. Nos. 3,098,755 and3,215,564. In this coating application process, the coating solution isapplied to a moving metal surface by means of a feed roller whosesurface is wetted with the coating solution and is rotating in adirection reversed or opposite to that in which the metal surface ismoving past the roller surface. This coating technique is particularlysuited to applying coating solution to metal in strip form.

The reverse roller coating technique has a number of advantages overother techniques for applying conversion coating solutions to metalsurfaces. For example, with respect to that method of applying thecoating solution by moving the metal surface past or over a roll orrollers which are rotating or moving in the same direction as the metalsurface, the reverse roller coating technique has the advantages thatthe coatings can be applied to the surface with greater rapidity andwithout sacrificing coating quality; in many applications, animprovement in coating quality is obtained. These advantages arerealized also when the reverse roller coating technique is compared withother application methods, such as spraying and immersion methods.

The use of reverse roller coating for the application of iron phosphatecoatings to ferriferous metals has been more difficult to achieve withconventional iron phosphating solutions then has the application ofother chemical coating systems by reverse roll coating. One reason isthat the residence time, or dwell time, of the solution in activecontact with the surface is inherently short in the reverse roll coatingmethod. Additionally, some difficulty has been encountered in obtainingthe necessary smooth spreading properties for the solutions when theyare applied by means of a roller. The compositions of the presentinvention overcome both of these problems and produce good qualityeffective iron phosphate coatings when applied by the reverse roll coatmethod.

From the foregoing discussion it can be seen that among the objects ofthe present invention are the following:

the provision of improved compositions and methods suitable for use incleaning of aluminum, which are especially useful in cleaning aluminumcans and the like in the course of manufacture;

The provision of improved compositions and methods for the cleaning,deoxidizing and brightening of stainless steel;

The provision of compositions and methods for the application of ironphosphate coatings to ferriferous surfaces by the use of reverse rollercoating techniques; and

The provision of novel compositions of wide versatility when used forthe treatment of metal surfaces.

The compositions of the present invention are multicom ponent systems,and for convenience the various components will be discussed separately,although it must be understood that the components do not function inisolation from one another, but cooperate to produce new and improvedresults discussed above.

In their preferred form, the compositions of the invention areconcentrates which may be diluted with water to a use concentrationappropriate for the particular application, but the invention may alsobe practiced by making solutions at use concentration directly from rawmaterials. The method aspects of the invention will be brought outfurther in the following claims.

The compositions of the invention are aqueous acidic solutionscontaining both phosphoric acid and sulphuric acid. By utilizing theseacids together, desirable effects are obtainable which are unavailableif only one is employed. Phosphoric acid is a desirable material fromthe standpoint of the cleaning utilities of the invention since it doesnot attack the metal cleaned (aluminum or stainless steel) or the metalnormally used in the cleaning equipment (stainless steel) as vigorouslyas the stronger inorganic acids which are used from time to time inacidic cleaners. In connection with the phosphate coating aspect of theinvention the phosphoric acid serves as a source for phosphate ion. Thesulphuric acid portion of the acid component serves in all of the usecontexts discussed above to lower the pH of the solutions, withoutcompletely obliterating the underlying character of the solutions asphosphate-type materials.

The use of a blend of phosphoric and sulphuric acid yields a number offurther advantages in the context of aluminum can cleaning, whencompared to other acidic aluminum cleaning compositions utilizingphosphoric acid only. The use of sulphuric acid with the phosphoric acidmakes possible the use of a relatively lower phosphate concentration,and, as pointed out above, results in a lower solution pH. These twocircumstances contribute materially to increasing the aluminum-carryingcapacity of the solution over earlier solutions using phosphoric acidonly. The term "aluminum-carrying capacity is an expression intended todescribe the ability of the solutions to hold aluminum in soluble form.When phosphoric acid based materials are used to clean aluminum, thesludge which will tend to form is aluminum phosphate, which is solublebelow a pH of about 2.0. The use of sulphuric acid in conjunction withphosphoric acid results in a solution having a normal pH below 2.0, thusincreasing the aluminum carrying capacity. In addition, since sulphuricacid serves as a source of hydrogen ions, relieving the phosphoric acidin part from this function, the relative phosphate concentration can belower, and the driving force for the formation of aluminum phosphate isreduced.

The lower pH obtained by the use of a combination of acids also reducesthe ability of the solution to emulsify oil, and as pointed out above,this is a desirable property when emulsifiable oils, such as drawingoils, are among the soils which must be removed from the aluminum.

Other advantages flow from the use of both sulfuric and phosphoric acidin the compositions of the invention. In aluminum cleaning, the cleanedsurfaces are bright even though sulphuric acid is used, by reason of thepresence of phosphoric acid. In addition, the blend of acids has aminimal rate of attack upon the washer equipment, which is ordinarilystainless steel.

In the context of stainless steel cleaning, deoxidizing and brightening,the blend of sulphuric and phosphoric acids is also superior to theperformance of either type of acid alone for the same purpose. Theaction of the solutions on stainless steel is faster than that ofsolutions based on phosphoric acid alone, but is not as severe as theaction resulting from the use of solutions based on sulphuric acidalone.

In accordance with the invention, not all blends or mixtures ofphosphoric and sulphuric acid yield the desirable results describedabove. At use concentrations, the acid component should be from about0.001 percent to about 0.005 percent for aluminum cleaning applications,from about 0.003 percent to about 0.015 percent for stainless steelcleaning and brightening applications, and from about 0.0015 percent toabout 0.015 percent for reverse roll iron phosphating applications.Within each of the foregoing ranges are preferred concentration rangesfor the acid component. For aluminum cleaning it is preferred that theconcentration be between about 0.0025 percent and 0.0035 percent, forstainless steel cleaning and brightening, between about 0.004 percentand about 0.0075 percent and for reverse roll iron phosphating betweenabout 0.0075 percent and about 0.0105 percent. The percentages justgiven are weight percentages calculated on the basis of 66 B. sulfuricacid and 75 percent phosphoric acid as acid sources. The foregoingdesirable effects have also been found to be dependent upon the ratiosof sulphuric acid to phosphoric acid. Such ratios may be mostconveniently expressed as volume ratios of sulphuric acid (as 66 8. H SOto phosphoric acid (as 75 percent H PO,). In such terms, the ratio ofsulphuric acid to phosphoric acid to produce the desired efi'ects runsbetween about 0.5 to 1 to about 1.5 to l, with a preferred ratio beingin the range of about 0.8 to l to about 1.2 to l.

A second component of the compositions of the invention is a surfactantcomponent. While various single surface active agents may be used aswell as many various blends of surface active agents, 1 have found thata blend of a primary ethoxylated alcohol sold under the name of Neodol-7, and a modified polyethyoxylated straight chain alcohol, sold underthe name of Triton DF-18, provides very satisfactory results in all ofthe above discussed areas of utility, especially in the aluminumcleaning context where an emulsifiable oil is present as a surface soil.For aluminum cleaning the total concentration of the surfactantcomponent should be from about 0.0010 percent to about 0.0035 percent byweight at use concentration and when the compositions of the inventionare used for cleaning and brightening stainless steel, the totalconcentration of the surfactant component should be from about 0.003percent to about 0.007 percent, again at use concentration. When thecompositions are used for iron phosphating by the reverse roll coatmethod, the surfactant component should be present in an amount fromabout 0.0013 percent to about 0.013 percent. When the preferredsurfactants just mentioned are employed, their weight ratio should befrom about 2.25 to about 1.75 to 1 expressed as primary ethoxylatedalcohol/modified polyethoxylated straight chain alcohol, for all threeof the applications.

Another component of the compositions of the present invention is termedhere a sequestrant component," since, in the various ways thecompositions are used, thesequestering action of the materials used inthis component appears to contribute materially to the overall action ofthe compositions. However, as brought out more fully below, thematerials in the sequestrant component also produce other desirableeffects. The sequestrant component of the present invention is made upof a blend of oxalic acid and citric acid. When the compositions of theinvention are used for aluminum cleaning, the total concentration of thesequestrant component (at use concentration) should be from about 0.001percent to about 0.002 percent by weight, and within these limits, thepreferred concentration is from about 0.0012 percent by weight to about0.0015 percent by weight. When the compositions are used for stainlesssteel cleaning and brightening, the concentration of the sequestrantcomponent should be from about 0.006 percent to about 0.0060 percent byweight, and when the compositions are used for reverse roll ironphosphating, the concentration of the sequestrant component should befrom about 0.0006 percent to about 0.0060 percent, again by weight. Thecombination of oxalic acid and citric acid appears to produce betterresults than that of either acid alone. Such improved results areobtained when the ratio of oxalic acid to citric acid is from about 2.25to 1 to about 1.75 to l, where the oxalic acid is expressed as oxalicacid dihydrate and the citric acid is expressed as anhydrous citricacid.

When the compositions of the present invention are used in aluminumcleaning, the sequestering component serves to increase the aluminumcarrying capacity of the solution, and in this connection cooperateswith the blend of acids of the acid component discussed above. Inaddition, the presence of citric acid in the sequestrant reduces thealuminum surface with satisfactory brightness. The oxalic acid, on theother hand, represses the corrosion rate of the solution on thestainless steel of the cleaning equipment. While the manner by which itdoes so is not fully understood, and there is no intention to be boundby a particular theory, it appears that the oxalic acid of thecomposition forms a very thin protective film on the stainless steelsurface and thus reduces the corrosion rate.

In the context of stainless steel cleaning and brightening, thesequestrant component functions to complex the dissolved oxides formingthe scale, and to prevent their redeposition on the metal surface. Inthe context of reverse roll iron phosphating, both the oxalic acid andthe citric acid contribute to dissolving the required amount of ironfrom the ferriferous surfaces being treated, and thus increase theferrous ion concentration at the coating site, so that a uniformphosphate coating will form in the short time available for itsformation inherent in the reverse roll ion phosphating method.

1n the preferred forms of the composition of the present invention, atemperature stabilizer is also included as a component. This mayconveniently be triethylene glycol. This component serves to stabilizethe concentrate when it is subjected to freezing conditions in thecourse of warehousing or shipping. In addition to lowering the freezingpoint of the aqueous concentrate, it also retards the formation ofprecipitates when the concentrate is repeatedly frozen and thawed. Suchprecipitates are undesirable since they subtract components from thesolution nonunifonnly and thus alter the balance of the solution, unlesscare is taken to bring the precipitates back into dissolved state beforeuse.

A preferred concentrate in accordance with the present invention has thefollowing formula:

The percentages of components listed above may be varied somewhat toproduce other concentrates, so long as care is taken to maintain theratios of materials forming each component within the ranges set outabove, and to maintain the proportion of each component so that upondilution to use concentration the above stated concentration ranges areachieved. In addition, as noted before, the temperature stabilizingmaterial (triethylene glycol) may be omitted if expected shipping andstorage conditions make it unnecessary.

When used for aluminum cleaning purposes, the foregoing concentrate ispreferably diluted with additional water in a ratio of about 1 partconcentrate to about 50 parts water, although good cleaning can beobtained over a dilution of from about 1 to 67 to about 1 to 40, thusproducing component ranges as discussed above. Best results are obtainedwhen the diluted solution is heated, and the preferred temperatureranges are from about 185 F., to about 195 F. At the preferred dilutionthe pH will be from about 1.4 to about 1.5 (measured at roomtemperature) and in any event it is preferred that the pH be kept wellbelow 2.0. Under these conditions, excellent cleaning of aluminumresults; even cans with emulsified drawing oil as one of the soils onthe surface, are very satisfactorily cleaned when exposed to a spray ofthe solution for a suitable time, such as about 60 seconds.

The above concentrate effectively descales, cleans and brightensstainless steel when it is diluted with water in a ratio of from about0.01 to 1 to about 0.05 to l. The descaling and cleaning is best carriedout when the solution is at a temperature of from about F. to about F.The length of treatment will depend to some extent upon the degree towhich the stainless steel is coated with annealing scale and other soil,but in general, if the solution is contacted with the stainless steelfor about 17 to 60 seconds, adequate cleaning and brightening will beobtained.

The preferred concentrate set forth above can be used to apply an ironphosphate coating to a ferriferous surface by the reverse roll coatmethod, and when it is so used, it is preferably diluted with water in aratio of from about 0.03 to l to about 0.05 to 1. The surface speed ofthe reverse roller in such an operation should be between about 51percent of the speed of the metal surface being coated, and a speed justinsufficient, in view of the diameter and rotational velocity of theroller, to cause solution to be thrown from the surface thereof bycentrifugal force (usually about 300 percent of the metal surfacespeed). The dwell time of the solution on the surface prior tosqueegeeing or wiping should be a minimum of about 5 seconds.

The data presented in table I below illustrates the improvement inresults obtained by the compositions of the present invention over theresults obtained by two operative prior art solutions, one based solelyon phosphoric acid and the other weight loss calculations for type 316stainless steel panels treated for hours in a vigorously stirred 1.5percent solution at l90200 F. Again, a low penetration represents goodperformance. The other dynamic corrosion tests are reported based solelyon sulphuric acid. The performance criteria used 5 under the columnheaded localized ebullition." in this test a to express the comparisonare formalized and quantitized 500 watt tubular heater was surrounded bya cylinder of type measures of the properties required for good aluminumcan 316 stainless steel tubing sized so that the annular space cleaning.Table I also illustrates the effect of varying the total between theheater and the cylinder had a thickness of apconcentration of an acidcomponent, as well as the efiect of proximately 1 millimeter. Thiscylinder was placed in two of varying the ratio of sulphuric acid tophosphoric acid. the solutions at a concentration of 1.5 percent and theheater in table 1 below the column headed Cleaning percent H O was usedto maintain the solution at 200-2l0 F. for 10 hours. Break reports thedegree to which the water breaks, that is, The solution was alsovigorously stirred. The penetration was the percentage of the surfacearea to which a thin continuous calculated from weight loss measurementson the stainless film of rinse water fails to adhere when the surface iscleaned l 5 steel cylinder. A low weight loss represents goodperformance. and then rinsed. The reported percentages in table Ireflect the it should be understood that the volume percents forrelative abilities of the solutions to clean aluminum so well Sulphuricacid and phosphoric acid reported in table I are exthat ordinary rinsewater forms a thin continuous sheet on the p 35 Percentages of Suchacids In the concentmle, and surface, and are based on a visualevaluation made when that all of the concentrates were used in the testsas 1.5 perdrawn and ironed aluminum cans were sprayed for about 55 centy Volume oft-he Solutionsseconds at about l80 F. and then rinsed. A lowpercent water SOIUUORS 1 through 9 of table I h as lhBI' mbreakrepresents a good cleaning performance by this ponents SurfactantSystems made P of P P f criterion, since discontinuities are caused byresidual oily tithoxylated alcohol (Neodol and Percent modified areaswhich were not removed by the solution during the PolyethoxylatedStraight Chain and a cleaning cycle. 25 sequestrant component consistingof oxalic acid dehydrate, The column headed Smut reports a visual ratingof the P and Citric add n y percent The degree of smut left on the anfter bei g l d i th balanceof each of the concentrates employed waswater. manner described above. The rating scale employed was as Solution10 ofthe table I had the formula! follows: was,

0 Trace l Shgh 75% phosphoric acid 25.97 2 Moderate 10% glycolic acid3.58 3 Heavy Primary ethoxylated alcohol The column headed Foam, mm.reports foam heights in 25-7) Modlfied polyethoxylated alcoholmillimeters for each sample at a 1.5 percent concentration (Triton M48)M3 when the foam was generated in a test machine designed fo Citric acidanhydrous 4.19 that purpose. This test machine is basically acylindrical conoxalic acid dihydrate 2- tainer with a spray impingementplate at the top thereof. A 3:12a 3-5: spray head is mounted to directsolution upwardly against the spray impingement plate. Solution is drawnfrom the bottom of the cylinder and pumped through the spray head at apres- Formula 11 fTabl 1 i d; sure of 20 psi. and at a selectedtemperature. After a period, a stable head of foam forms on top of thesolution in the cylinder, and it is the height of this foam layer whichis reported in table l. A low foam height is desirable. Ammonium f p fTechnical The column in table I headed Aluminum Dissolution g n ctylphenoxy polyethoxycthanol 0.8 Rate reports in milligrams per square footper mtnute the (Triton X402) weight loss of aluminum cans cleaned forone minute at 180 Wr ter 01.9

TABLE I Dynamic corrosion tests Volume, percent Cleaning Foam, mm.Aluminum dissolution Static Localized Percent rate, mg/. eorr Stirring,ebullitlon, H2804 H3PO4 H2O break Smut 140 F. 180 F. Itfl/min. mil/yrmil/yr. mil/yr.

14 6 8O 1 44 12 15.38 12 8 70 2 12 14.73 10 10 30 1 52 14 17. 8 12 40 247 11 19.28 0 14 10 1 50 9 20.00 4 16 20 2 35 12 19. 7B 7. 5 7.5 5 0 406 13. 6.0 9.0 10 1 47 5 15.05 4. 5 10. 6 5 0 66 10 12. 63 19 80 1 61 1310.09 11 80 3 05 18 9.07 Water 5. 50

F. with a spray pressure of 20 psi. A low aluminum dissolu- The data oftable I illustrates and emphasizes some of the tion rate represents goodperformance. points made in the discussion above. For example, fonnula[1,

The column headed Static Corrosion represents the the sulphuric acidbased solution, displays a relatively low alupcnetration, expressed inmils per year, calculated from minum dissolution rate, but it is arelatively poor cleaner with weight loss mcatsurcmcnts made on type 316stainless steel 70 a high water break and an objectionable amount ofsmut. ln

coupons treated with l.5 percent solutions at 188 F. for 139 hours. Alow static corrosion rate is a desirable property.

For some of the solutions there are reported in table I the results oftwo types of dynamic corrosion tests. In the stirring addition, thesolution is objectionably corrosive to stainless steel. The other priorart solution, formula 10, which is based solely on phosphoric acid, issomewhat better as a cleaner than formula II, but has a significantlyhigher aluminum distest, the penetration in mils per year is reported,based on solution rate and a relatively high rate of attack or corrosionon stainless steel. In addition, it shows a weakness in cleaning abilityin that it has a relatively high water break.

By contrast, solutions containing both acids show good cleaningperformance with respect to smut in all cases, and as the preferredconcentrations and acid ratios are approached, a material improvement incleaning performance as measured by water break. Even formula 1, thepoorest of the acid blends, showed a water break property equal to bothformulas 10 and 11.

Fonnulas 7, 8 and 9, which represent the preferred ranges and acidratios for aluminum cleaning, are far superior to prior art formulas land 1 l with respect to stainless steel corrosion (static and dynamic),are far superior in cleaning ability as measured by smut, are lowerfoaming, and have acceptable aluminum dissolution rates which are higherthan that of formula 11, but lower than that of formula 10. The overallperformance of formula 7 was the best.

Table II below reports a comparison between formula 7 of the inventionand prior art solution fonnula 10 with respect to aluminum carryingcapacity. In this experiment, the surfactant component was omitted fromboth solutions to prevent it from masking detection of precipitate.Aluminum was suspended in 1 9% percent solutions of concentrates 7 and10 and the solution was heated to 200 F. by an electric heater with astainless steel jacket. The heater was frequently partially removed fromthe test bath and inspected to determine the point at whichprecipitation in the form of scale started to appear on the stainlesssteel jacket, and the aluminum concentration was measured when suchprecipitation first occurred. As table II shows, the aluminum carryingcapacity in grams/liter of formula 7 was nearly three times that offormula 10.

TABLE 11 Aluminum Concentration Formula Vol. 56 Vol. I: whenprecipitation began H,SO, H,PO, g./l.

The use of the compositions of the present invention for cleaning,deoxidizing, and brightening stainless steel is illustrated by thefollowing example:

EXAMPLE I EXAMPLE II Steel coupons were processed on a pilot scalereverse roll coating apparatus operated at a metal surface speedequivalent to 150 feet per minute, with the reverse roller surface speedequal to 100 percent of the metal surface speed. A percent aqueoussolution was applied to the steel surface by the reverse roller, andallowed to dwell on the surface for 6 seconds. After squeegeeing,rinsing and drying, the coupons were painted and then subjected to astandard cup and ball impact test for paint adhesion. The paint adhesionas so measured was equivalent to results generally obtained whenconventional iron phosphate solutions applied to steel in a conventionalmanner are evaluated under paint in the same way.

The preferred concentrate was used tion.

From the foregoing it can be seen that in accordance with the presentinvention compositions of great versatility are provided for use intreating metal surfaces.

I claim:

1. A concentrated composition suitable, upon dilution with water, forcleaning of aluminum surfaces, for deoxidizing and cleaning of stainlesssteel, and for forming an iron phosphate coating on ferriferoussurfaces, comprising an aqueous solution of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to 1 to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid);

a surfactant component;

and a sequestrant component consisting of oxalic acid and to form 5percent solucitric acid in a weight ratio of from about 2.25 to l toabout 1.75 to 1 (calculated as oxalic acid dihydrate/anhydrous citricacid);

said components being present in the concentrate in amounts sufficient,upon dilution of the concentrate with water, to produce a solution forcleaning aluminum in which the concentration of the acid component isbetween about 0.001 percent and about 0.005 percent by weight, theconcentration of the surfactant component is between about 0.0010percent and about 0.0035 percent by weight, and the concentration of thesequestrant component is between about 0.001 percent and 0.002 percentby weight, and to produce a solution for cleaning and deoxidizingstainless steel in which the concentration of the acid component isbetween about 0.003 percent and about 0.015 percent by weight, theconcentration of the surfactant component is between about 0.003 percentand about 0.007 percent by weight, and concentration of the sequestrantcomponent is between about 0.0006 percent and about 0.0060 percent byweight, and further to produce an iron phosphating solution in which theconcentration of the acid component is between about 0.0015 percent andabout 0.015 percent by weight, the concentration of the surfactantcomponent is between about 0.0013 percent and about 0.013 percent byweight, and the concentration of the sequestrant component between about0.0006 percent and about 0.0060 percent by weight. 7

2. A composition according to claim 1 in which the volume ratio ofsulfuric acid and phosphoric acid in said acid component is betweenabout 0.8 to 1 and about 1.2 to 1, (calculated as 66 B. sulfuric acid/75percent phosphoric acid).

3. A composition according to claim 1 in which said surfactant componentconsists of primary ethoxylated alcohol and modified polyethoxylatedstraight chain alcohol.

4. A composition according to claim 3 in which the weight ratio ofprimary ethoxylated to modified polyethoxylated straight chain alcoholis between about 2.25 to 1 to about 1 .75 to 1.

5. A composition according to claim 1 and further comprising about 1percent tri ethylene glycol.

6. A concentrate useful upon dilution with water for treatment of metalsurfaces consisting essentially of an aqueous solution containing about11 percent by weight phosphoric acid (calculated as 75 percentphosphoric acid), about 12.8 percent by weight sulfuric acid (calculatedas 66 B. sulfuric acid), about 8.0 percent by weight primary ethoxylatedalcohol, about 4.6 percent modified polyethoxylated straight chainalcohol, about 2.0 percent by weight oxalic acid (calculated as oxalicacid dihydrate) and about 4.2 percent by weight citric acid (calculatedas anhydrous citric acid).

7. A concentrate according to claim 6 and further containing about 1percent tri ethylene glycol.

8. A solution for cleaning aluminum surfaces comprising an aqueoussolution consisting essentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to 1 to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.001 percent and about 0.005 percentby weight,

a surfactant component in an amount between about 0.0010 percent and0.0035 percent by weight,

and a sequestrant component consisting of oxalic acid and citric acid ina weight ratio of from about 2.25 to l to about 1.75 to 1 (calculated asoxalic acid dihydrate/anhydrous citric acid), the concentration of saidsequestrant component being between about 0.001 percent and about 0.002percent by weight.

9. A solution in accordance with claim 8 in which the concentration ofsaid acid component is between about 0.0025 percent and about 0.0035percent by weight.

10. A solution in accordance with claim 8 in which the surfactantcomponent consists of primary ethoxylated alcohol and modifiedpolyethoxylated straight chain alcohol in a ratio offrom about 2.25 to lto about 1.75 to 1.

11. A solution in accordance with claim 8 in which the concentration ofsaid sequestrant component is between about 0.0012 percent and about0.0015 percent by weight.

12. A solution for cleaning deoxidizing and brightening stainless steelcomprising an aqueous solution consisting essentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to l to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.003 percent and about 0.015 percentby weight,

a surfactant component in an amount between about 0.003

percent and about 0.007 percent by weight, and a sequestrant componentconsisting of oxalic acid and citric acid in a weight ratio of fromabout 2.25 to l to about 1.75 to 1 (calculated as oxalic aciddihydrate/anhydrous citric acid), the concentration of said sequestrantcomponent being between about 0.0006 percent and about 0.0060 percent byweight. 13. A solution in accordance with claim 12 in which theconcentration of said acid component is between about 0.004 percent andabout 0.0075 percent by weight.

14. A solution in accordance with claim 12 in which the surfactantcomponent consists of primary ethoxylated alcohol and modifiedpolyethoxylated straight chain alcohol in a ratio of from about 2.25 tol to about 1.75 to 1.

15. A solution for applying an iron phosphate coating to ferriferoussurfaces comprising an aqueous solution consisting essentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to l to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.0015 percent and about 0.015percent by weight,

a surfactant component in an amount between about 0.0013 percent andabout 0.013 percent by weight,

and a sequestrant component consisting of oxalic acid and citric acid ina weight ratio of from about 2.25 to l to about 1.75 to 1 (calculated asoxalic acid dihydrate/anhydrous citric acid), the concentration of saidsequestrant component being between about 0.0006 percent and about0.0060 percent by weight.

16. A solution in accordance with claim 15 in which the concentration ofsaid acid component is between about 0.0075 percent and and about 0.0105percent by weight.

17 A solution in accordance with claim 15 in which the surfactantcomponent consists of primary ethoxylated alcohol and modifiedpolyethoxylated straight chain alcohol in a ratio of from about 2.25 tol to about 1.75 to 1.

18. A method for cleaning aluminum surfaces comprising contacting saidsurfaces with an aqueous solution consisting essentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume of from about 0.5 to l to about 1.5 to 1, (calculated as 66 B.sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.001 percent and about 0.005 percentby weight,

a surfactant component in an amount between about 0.0010 percent andabout 0.0035 percent by weight,

and a sequestrant component consisting of oxalic acid and citric acid ina weight ratio of from about 2.25 to 1 to about 1.75 to 1, (calculatedas oxalic acid dihydrate/anhydrous citric acid), the concentration ofsaid sequestrant component being between about 0.001 percent and about0.002 percent by weight, and thereafter rinsing said surfaces.

19. A method for cleaning deoxidizing and brightening stainless steelsurfaces comprising contacting said surfaces with an aqueous solutionconsisting essentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to l to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.003 percent and about 0.0015percent by weight,

a surfactant component in an amount between about 0.003

percent and about 0.007 percent by weight, and a sequestrant componentconsisting of oxalic acid and citric acid in a weight ratio of fromabout 2.25 to l to about 1.75 to 1, (calculated as oxalic aciddihydrate/anhydrous citric acid), the concentration of said sequestrantcomponent being between about 0.0006 percent and about 0.0060 percent byweight. 20. A method for applying an iron phosphate coating toferriferous surfaces comprising applying by a reverse contact roll to amoving ferriferous surface and an aqueous solution consistingessentially of:

an acid component consisting of sulfuric acid and phosphoric acid in avolume ratio of from about 0.5 to l to about 1.5 to 1, (calculated as 66B. sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.0015 percent and about 0.015percent by weight,

a surfactant component in an amount between about 0.0013 percent andabout 0.013 percent by weight,

and a sequestrant component consisting of oxalic acid and citric acid ina weight ratio of from about 2.25 to l to about 1.75 to 1, (calculatedas oxalic acid dihydrate/ anhydrous citric acid), the concentration ofsaid sequestrant component being between about 0.0006 percent and about0.0060 percent by weight, and allowing said solution to dwell on saidsurface for at least 5 seconds.

UNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION Patent No. 3 35 i75 Dated Januarv l8 19 72 Invent r( Andrew J. Hamilton It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

IN SPECIFICATION Column 3, line 39, "the" should read -The- Column 3,line 5 4, after "produce", read--the-.

Column 3, line 63, "claims" should read -discussion--.

Column 4, line 60, and line 68, "B." should read ---Be 7 Column 5, line42, "0.006", first occurrence, should read-0.000E

Column 6, line 19, "B." should read --Be-.

Column 8, line +6, "B." should read -Be IN THE CLAIMS In each of thefollowing claims, "B." should read --Be Claim 1, line 8; Claim 6, line5; Claim 8, line 5; Claim 12, line Claim 15, line 6; Claim 18, line 6;Claim 19, line 6; Claim 20, line 7.

Claim 19 line 9 "0.0015", should read --0 .015.

Signed and sealed this L th day of July 1972.

(SEAL) Attest EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK AttestingOfficer Commissioner of Patents FORM PC40 (10-69) USCOMM-DC 60376-P69 flU.S. GOVERNMENT PRINTING OFFICE: 1968 0-366-334

2. A composition according to claim 1 in which the volume ratio ofsulfuric acid and phosphoric acid in said acid component is betweenabout 0.8 to 1 and about 1.2 to 1, (calculated as 66* B. sulfuricacid/75 percent phosphoric acid).
 3. A composition according to claim 1in which said surfactant component consists of primary ethoxylatedalcohol and modified polyethoxylated straight chain alcohol.
 4. Acomposition according to claim 3 in which the weight ratio of primaryethoxylated to modified polyethoxylated straight chain alcohol isbetween about 2.25 to 1 to about 1.75 to
 1. 5. A composition accordingto claim 1 and further comprising about 1 percent tri ethylene glycol.6. A concentrate useful upon dilution with water for treatment of metalsurfaces consisting essentially of an aqueous solution containing about11 percent by weight phosphoric acid (calculated as 75 percentphosphoric acid), about 12.8 percent by weight sulfuric acid (calculatedas 66* B. sulfuric acid), about 8.0 percent by weight primaryethoxylated alcohol, about 4.6 percent modified polyethoxylated straightchain alcohol, about 2.0 percent by weight oxalic acid (calculated asoxalic acid dihydrate) and about 4.2 percent by weight citric acid(calculated as anhydrous citric acid).
 7. A concentrate according toclaim 6 and further containing about 1 percent tri ethylene glycol.
 8. Asolution for cleaning aluminum surfaces comprising an aqueous solutionconsisting essentially of: an acid component consisting of sulfuric acidand phosphoric acid in a volume ratio of from about 0.5 to 1 to about1.5 to 1, (calculated as 66* B. sulfuric acid/75 percent phosphoricacid), the concentration of said acid component being between about0.001 percent and about 0.005 percent by weight, a surfactant componentin an amount between about 0.0010 percent and 0.0035 percent by weight,and a sequestrant component consisting of oxalic acid and citric acid ina weight ratio of from about 2.25 to 1 to about 1.75 to 1 (calculated asoxalic acid dihydrate/anhydrous citric acid), the concentration of saidsequestrant component being between about 0.001 percent and about 0.002percent by weight.
 9. A solution in accordance with claim 8 in which theconcentration of said acid component is between about 0.0025 percent andabout 0.0035 percent by weight.
 10. A solution in accordance with claim8 in which the surfactant component consists of primary ethoxylatedalcohol and modified polyethoxylated straight chain alcohol in a ratioof from about 2.25 to 1 to about 1.75 to
 1. 11. A solution in accordancewith claim 8 in which the concentration of said sequestrant component isbetween about 0.0012 percent and about 0.0015 percent by weight.
 12. Asolution for cleaning deoxidizing and brightening stainless steelcomprising an aqueous solution consisting essentially of: an acidcomponent consisting of sulfuric acid and phosphoric acid in a volumeratio of from about 0.5 to 1 to about 1.5 to 1, (calculated as 66* B.sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.003 percent and about 0.015 percentby weight, a surfactant component in an amount between about 0.003percent and about 0.007 percent by weight, and a sequestrant componentconsisting of oxalic acid anD citric acid in a weight ratio of fromabout 2.25 to 1 to about 1.75 to 1 (calculated as oxalic aciddihydrate/anhydrous citric acid), the concentration of said sequestrantcomponent being between about 0.0006 percent and about 0.0060 percent byweight.
 13. A solution in accordance with claim 12 in which theconcentration of said acid component is between about 0.004 percent andabout 0.0075 percent by weight.
 14. A solution in accordance with claim12 in which the surfactant component consists of primary ethoxylatedalcohol and modified polyethoxylated straight chain alcohol in a ratioof from about 2.25 to 1 to about 1.75 to
 1. 15. A solution for applyingan iron phosphate coating to ferriferous surfaces comprising an aqueoussolution consisting essentially of: an acid component consisting ofsulfuric acid and phosphoric acid in a volume ratio of from about 0.5 to1 to about 1.5 to 1, (calculated as 66* B. sulfuric acid/75 percentphosphoric acid), the concentration of said acid component being betweenabout 0.0015 percent and about 0.015 percent by weight, a surfactantcomponent in an amount between about 0.0013 percent and about 0.013percent by weight, and a sequestrant component consisting of oxalic acidand citric acid in a weight ratio of from about 2.25 to 1 to about 1.75to 1 (calculated as oxalic acid dihydrate/anhydrous citric acid), theconcentration of said sequestrant component being between about 0.0006percent and about 0.0060 percent by weight.
 16. A solution in accordancewith claim 15 in which the concentration of said acid component isbetween about 0.0075 percent and and about 0.0105 percent by weight. 17A solution in accordance with claim 15 in which the surfactant componentconsists of primary ethoxylated alcohol and modified polyethoxylatedstraight chain alcohol in a ratio of from about 2.25 to 1 to about 1.75to
 1. 18. A method for cleaning aluminum surfaces comprising contactingsaid surfaces with an aqueous solution consisting essentially of: anacid component consisting of sulfuric acid and phosphoric acid in avolume of from about 0.5 to 1 to about 1.5 to 1, (calculated as 66* B.sulfuric acid/75 percent phosphoric acid), the concentration of saidacid component being between about 0.001 percent and about 0.005 percentby weight, a surfactant component in an amount between about 0.0010percent and about 0.0035 percent by weight, and a sequestrant componentconsisting of oxalic acid and citric acid in a weight ratio of fromabout 2.25 to 1 to about 1.75 to 1, (calculated as oxalic aciddihydrate/anhydrous citric acid), the concentration of said sequestrantcomponent being between about 0.001 percent and about 0.002 percent byweight, and thereafter rinsing said surfaces.
 19. A method for cleaningdeoxidizing and brightening stainless steel surfaces comprisingcontacting said surfaces with an aqueous solution consisting essentiallyof: an acid component consisting of sulfuric acid and phosphoric acid ina volume ratio of from about 0.5 to 1 to about 1.5 to 1, (calculated as66* B. sulfuric acid/75 percent phosphoric acid), the concentration ofsaid acid component being between about 0.003 percent and about 0.0015percent by weight, a surfactant component in an amount between about0.003 percent and about 0.007 percent by weight, and a sequestrantcomponent consisting of oxalic acid and citric acid in a weight ratio offrom about 2.25 to 1 to about 1.75 to 1, (calculated as oxalic aciddihydrate/anhydrous citric acid), the concentration of said sequestrantcomponent being between about 0.0006 Percent and about 0.0060 percent byweight.
 20. A method for applying an iron phosphate coating toferriferous surfaces comprising applying by a reverse contact roll to amoving ferriferous surface and an aqueous solution consistingessentially of: an acid component consisting of sulfuric acid andphosphoric acid in a volume ratio of from about 0.5 to 1 to about 1.5 to1, (calculated as 66* B. sulfuric acid/75 percent phosphoric acid), theconcentration of said acid component being between about 0.0015 percentand about 0.015 percent by weight, a surfactant component in an amountbetween about 0.0013 percent and about 0.013 percent by weight, and asequestrant component consisting of oxalic acid and citric acid in aweight ratio of from about 2.25 to 1 to about 1.75 to 1, (calculated asoxalic acid dihydrate/ anhydrous citric acid), the concentration of saidsequestrant component being between about 0.0006 percent and about0.0060 percent by weight, and allowing said solution to dwell on saidsurface for at least 5 seconds.